Gyrostabilisers

ABSTRACT

A gyrostabiliser having a vacuum chamber assembly is disclosed. The gyrostabilizer can have a flywheel enclosed within a vacuum chamber formed by a housing. The flywheel shaft can be fixed to or integral with the flywheel and located relative to the housing by upper and lower spin bearings which permit rotation of the flywheel about the spin axis.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Australian Provisional PatentApplication No. 2016903303, filed Aug. 19, 2016, which is incorporatedherein in its entirety.

TECHNICAL FIELD

The present invention relates to gyrostabilisers and specificallyrelates to the lubrication of the spin axis bearings.

BACKGROUND

Gyrostabilisers for stabilising bodies, such as for example marinevessels, are well known. Such gyrostabilisers include a flywheel which,in use, spins about a spin axis at a high rotational speed of typicallythree thousand to ten thousand revolutions per minute. The flywheel spinaxis is held in a gimbal frame having a gimbal shaft or precession axisperpendicular to the spin axis, with the precession motions being brakedand/or driven. Due to the high velocity of the outer rim of theflywheel, the gimbal frame is typically a chamber enclosing the flywheelto enable the flywheel to spin within a vacuum. This reduces drag whichreduces heat generation and improves efficiency. The spin bearings usedto locate the flywheel about the spin axis are subject to both highloads and high rotational speeds which also generate heat and noise.

The spin bearings and spin motor are usually located within the vacuumchamber to avoid issues associated with sealing the vacuum chamber wherethe spin shaft exits the vacuum chamber. Having the spin bearings withinthe vacuum chamber makes lubricating and cooling of the spin bearingsdifficult. It is even more difficult to cool the inner races of the spinbearings and the flywheel shaft because these are rotating and cannoteasily be cooled by contact with a coolant jacket. The spin bearings aretypically roller bearings lubricated by grease, although the use ofplain bearings and of oil bath lubrication in nominally horizontal spinaxis gyrostabilisers is known. However, recirculating oil systems arenot used, partly because pumping oil into and out of a vacuum isdifficult. Cooling fins and/or cooling jackets can be provided to assistcooling of the bearings and vacuum chamber, but even using a coolingjacket to cool the bearings does not provide effective cooling of thecomplete bearing.

The present invention was developed with a view to providing improvedlubrication and/or cooling of the spin bearings of a gyrostabiliser.

The issues associated with sealing the vacuum chamber where the spinshaft exits the vacuum chamber are due to the high radial forces on theflywheel shaft. These high radial forces require a flywheel shaft ofsuch a large diameter that the surface speed of a shaft seal is high,and also create a large radial movement or run-out at the shaft seal,the combination resulting in a seal with at least some leakage.

It has been found desirable that the present invention may furtherprovide a lubrication arrangement that is tolerant of leakage of oilinto the vacuum chamber.

SUMMARY

According to a first aspect of the invention there is provided agyrostabiliser including a vacuum chamber assembly including: a flywheelenclosed within a vacuum chamber formed by a housing; a flywheel shaftfixed to or integral with the flywheel and located relative to thehousing by upper and lower spin bearings which permit rotation of theflywheel about the spin axis, wherein, the vacuum chamber assemblyfurther includes: an upper spin bearing chamber and an upper shaft sealaround the flywheel shaft, the upper spin bearing chamber accommodatingthe upper spin bearing, and being separated from the vacuum chamber bythe upper shaft seal; a lower spin bearing chamber and a lower shaftseal around the flywheel shaft, the lower spin bearing chamberaccommodating the lower spin bearing, and being separated from thevacuum chamber by the lower shaft seal; and wherein the gyrostabiliserincludes an oil circuit having at least one outlet into the upper spinbearing chamber, at least one drain out of the upper spin bearingchamber, at least one outlet into the lower spin bearing chamber and atleast one drain out of the lower spin bearing chamber.

Preferably, the upper spin bearing chamber is formed at least in part bythe housing. Preferably, the lower spin bearing chamber is formed atleast in part by the housing. The upper spin bearing chamber and/or thelower spin bearing chamber may be provided in a respective bearingcarrier.

The vacuum chamber may, in use, be at a pressure of less than minus 0.8bar gauge (barg), preferably less than minus 0.9 bar gauge (barg), andmore preferably less than minus 0.95 bar gauge (barg).

The upper and lower spin bearing chambers may, in use, be at a pressureof between minus 0.2 bar gauge (barg) and minus 0.8 bar gauge (barg),preferably between minus 0.3 bar gauge (barg) and minus 0.7 bar gauge(barg), and more preferably between minus 0.4 bar gauge (bag) and minus0.6 bar gauge (barg).

Alternatively, the vacuum chamber may be at a pressure of less than 600Torr (or 600 mmHg), although to reduce drag and heat generated byflywheel rotation the pressure in the vacuum chamber may preferably beless than 200 Torr and more preferably less than 50 Torr.

The pressure in the upper and lower spin bearing chambers may be betweenatmospheric pressure and vacuum chamber pressure, but preferably notless than 150 Torr to remain in an operating range of most pumps. So,for example, the pressure in the vacuum chamber and the spin bearingchambers can all be substantially equal at, for example, approximately300 Torr, or preferably approximately 200 Torr.

Each of the at least one outlet may include or be at least one nozzle.The at least one outlet into the upper spin bearing chamber may includeat least one oil jet or spray directed onto the upper spin bearing, suchas by the at least one nozzle.

Additionally, or alternatively, the at least one outlet into the upperspin bearing chamber may include at least one oil jet or spray directedonto the upper shaft seal.

Additionally, or alternatively, the at least one outlet into the lowerspin bearing chamber may include at least one oil jet or spray directedonto the lower spin bearing.

The lower spin bearing may include a first lower spin bearing and asecond lower spin bearing, and the at least one outlet into the lowerspin bearing chamber may include at least one oil jet or spray directedonto the first lower spin bearing and/or at least one oil jet or spraydirected onto the second lower spin bearing.

Additionally, or alternatively, the at least one outlet into the lowerspin bearing chamber may include one or more respective oil jet or spraydirected onto the lower shaft seal.

The oil circuit may include at least one filter.

In one or more forms of the present invention the gyrostabiliser mayfurther include an oil collection chamber, an oil reservoir, at leastone return oil pump and a supply oil pump.

The oil reservoir may function as a contaminant settling tank,de-aeration tank, passive cooling tank and/or reservoir for maintenance,for example.

The oil collection chamber may be provided at least in part by thehousing.

The at least one drain out of the upper spin bearing chamber and the atleast one drain out of the lower spin bearing chamber may preferably beconnected to the oil collection chamber.

A radial throwing disc may be located in the oil collection chamber,preferably fixed to or driven by the flywheel shaft, although it can bedriven by any known means.

The radial throwing disc is provided to throw or urge oil toward radialports on the oil collection chamber, the radial ports being connected tothe at least one return oil pump.

The oil circuit may include: the oil reservoir; the supply pumpconnected between the oil reservoir and the at least one outlet intoeach bearing chamber; a drain conduit connecting the at least one drainout of the upper spin bearing chamber to the oil collection chamber anda drain path from the at least one drain out of the lower spin bearingchamber to the oil collection chamber; the at least one return oil pumpbeing provided to pump oil from the oil collection chamber to the oilreservoir.

The at least one return oil pump may be located in the oil collectionchamber, for example the at least one return oil pump may be driven bythe flywheel shaft. Such a flywheel shaft driven pump may be of thegear, screw, diaphragm or piston type for example.

Alternatively, the at least one return oil pump may be connected betweenthe oil collection chamber and the oil reservoir and could beelectrically driven. When the pump is not located in the oil collectionchamber, the use of the optional radial throwing disc can be beneficialto help prime the inlet of the pump with oil.

The gyrostabiliser may further include an oil cooler. For example, theoil cooler may include a radiator located in the oil circuit, or includea passive tank the walls of which radiate heat energy from the oil.

The passive tank may, for example, be the oil reservoir and, asmentioned above, may allow particulates and air bubbles to settle out,or may preferably include a heat exchanger having an oil portion formingpart of the oil circuit e.g. oil is pumped through the heat exchanger,for example, between the reservoir and the outlets, and a coolantportion through which water or coolant flows or is pumped.

The gyrostabiliser may further include a vacuum chamber oil scavengecavity located in the housing towards the bottom of the vacuum chamber.

The vacuum chamber oil scavenge cavity may be connected to the oilcollection chamber by a pumping arrangement to enable oil to be pumpedout of the vacuum chamber and ultimately returned to the oil reservoir.

The pumping arrangement may include: an intermediate tank; a lower valvefor selectively communicating the intermediate tank to the oilcollection chamber; an upper valve for selectively communicating thevacuum chamber oil scavenge cavity to the intermediate tank; and apressure switching valve for selectively communicating the intermediatetank with the vacuum chamber or atmosphere.

The gyrostabiliser may further include a coolant circuit including: acoolant pump; a coolant reservoir: at least one oil heat exchanger; anda water heat exchanger, preferably a sea water heat exchanger. The watermay be salt water or fresh water.

The coolant circuit may further include a cooling jacket for the upperspin bearing and/or a cooling jacket for the lower spin bearing.Similarly, the coolant circuit may further include a cooling plate orjacket for a spin motor and optionally a spin motor drive.

The coolant circuit may further include one or more cooling plates orjackets for at least one precession control motor(s) and precessionmotor drive(s). Additionally, or alternatively, the coolant circuit mayfurther include a cooling jacket for the spin braking resistor.

The coolant circuit may further include a bypass conduit or passage inparallel with a coolant flow path through the water heat exchanger and abypass valve for controlling the balance of coolant flow through thebypass conduit or passage and through the coolant flow path through thewater heat exchanger.

Preferably, the balance of coolant flow through the water heat exchangerversus through the bypass conduit or passage is controlled as a functionof the temperature of the coolant at or near a coolant inlet to thewater heat exchanger.

The at least one oil heat exchanger may include a lubrication oil heatexchanger having an oil inlet and an oil outlet forming part of the oilcircuit, in addition to and separate from a coolant flow path throughthe lubrication oil heat exchanger including a coolant inlet and acoolant outlet. In this instance, the oil is the oil lubricating thespin bearings.

The lubricating oil heat exchanger may be the aforementioned oil cooler.

Additionally, or alternatively, the at least one oil heat exchanger mayinclude a hydraulic oil heat exchanger having a hydraulic oil inlet anda hydraulic oil outlet forming part of a hydraulic circuit including ahydraulic manifold, in addition to and separate from a coolant flow paththrough the hydraulic oil heat exchanger including a coolant inlet and acoolant outlet. In this instance the oil is hydraulic oil from forexample a precession control arrangement.

The gyrostabiliser may further include an air circuit including: avacuum pump in fluid communication with the vacuum chamber; and an airdryer.

The air circuit may further include a vent relief valve connected by areservoir pressure conduit to a port at or toward a top of the oilreservoir.

The air circuit may further include a pressure regulating valveconnected between the reservoir pressure conduit and a port on thehousing. For example, the port on the housing may be into the upper spinbearing chamber and/or and lower spin bearing chamber.

The pressure regulating valve may only permit flow from the reservoirpressure conduit into the port on the housing when a pressure dropacross the pressure regulating valve is greater than a pre-setmagnitude, such as, for example, approximately 0.7 bar.

The air circuit may further include an oil trap in the reservoirpressure conduit between the vent relief valve and the oil reservoir,the pressure regulating valve being connected to the reservoir pressureconduit by a port toward a base of the oil trap. Then the pressureregulating valve can facilitate return of oil from the oil trap backinto the oil circuit by permitting flow from the oil trap to a port onthe housing, the port on the housing being for example into the upperspin bearing chamber and/or and lower spin bearing chamber.

The air circuit may further include a bleed back check valve between thereservoir pressure conduit and the air dryer.

The air circuit may in addition to the aforementioned pressure switchingvalve and intermediate tank further include: a conduit connecting thepressure switching valve to the air dryer; a conduit connecting thepressure switching valve to the intermediate tank; and a conduitconnecting the pressure switching valve to the vacuum chamber.

Another aspect of the present invention provides a lubricationarrangement for a vacuum chamber assembly for a gyrostabiliser, thevacuum chamber assembly including: a flywheel enclosed within a vacuumchamber formed by a housing; a flywheel shaft fixed to or integral withthe flywheel and located relative to the housing by upper and lower spinbearings which permit rotation of the flywheel about the spin axis; anupper spin bearing chamber and an upper shaft seal around the flywheelshaft, the upper spin bearing chamber accommodating the upper spinbearing, and being separated from the vacuum chamber by the upper shaftseal; a lower spin bearing chamber and a lower shaft seal around theflywheel shaft, the lower spin bearing chamber accommodating the lowerspin bearing, and being separated from the vacuum chamber by the lowershaft seal; the lubrication arrangement including at least one oil jetor spray into the upper spin bearing chamber and at least one oil jet orspray into the lower spin bearing chamber.

As mentioned above, preferably, the upper spin bearing chamber is formedat least in part by the housing.

Preferably, the lower spin bearing chamber is formed at least in part bythe housing.

The upper spin bearing chamber and/or the lower spin bearing chamber maybe provided in a respective bearing carrier.

Another aspect of the present invention provides a system forlubricating a spin bearing of a gyrostabiliser, the system including alubrication circuit, a coolant circuit and an air circuit.

The lubrication circuit may include at least one jet or spray forreleasing lubricating oil into a bearing chamber housing of the spinbearing.

The coolant circuit may include at least one lubricating oil heatexchanger for drawing heat out of the lubricating oil of the lubricatingcircuit.

Alternatively, or additionally, the coolant circuit may include a pumpand a water heat exchanger for drawing heat out of coolant in thecoolant circuit.

The air may circuit include a vacuum pump and valves wherein the valvescontrol a pressure in the bearing chamber to be between a pressure in avacuum chamber of the gyrostabiliser and an atmospheric pressure.

The system may further include an intermediate tank having an upper oilport and an upper air port for example located at or towards a top ofthe intermediate tank, a lower oil port located at or toward a base ofthe intermediate tank and a level sensor; the lubrication circuit mayinclude a first lockout valve between the upper oil port of theintermediate tank and a port towards a bottom of a vacuum chamber of thegyrostabiliser and a second lockout valve between the lower oil port ofthe intermediate tank and an oil collection chamber of thegyrostabiliser; the air circuit may include a pressure switching valveto selectively communicate a conduit connected to the upper air port ofthe intermediate tank to either the vacuum chamber of the gyrostabiliseror to atmosphere, preferably via an air dryer.

It will be convenient to further describe the invention by reference tothe accompanying drawings which illustrate preferred embodiments of thepresent invention.

Other embodiments of the present invention are possible and consequentlyparticularity of the accompanying drawings is not to be understood assuperseding the generality of the preceding description of theinvention.

BRIEF DESCRIPTION OF DRAWINGS

In the drawings:

FIG. 1 is a cut away perspective view of a gyrostabiliser vacuumchamber.

FIG. 2 is a schematic view of an oil circuit according to an embodimentof the present invention.

FIG. 3 is a schematic view of an air circuit according to an embodimentof the present invention.

FIG. 4 is a schematic view of a coolant circuit according to anembodiment of the present invention.

DETAILED DESCRIPTION

Referring initially to FIG. 1, there is shown the vacuum chamberassembly 10 of a gyrostabiliser. The flywheel 11 is housed in the vacuumchamber 12 or flywheel chamber, formed within the housing 13. Thehousing is pivotally mounted on precession bearing stubs 14 fixed to thehousing 13, with the precession bearings 15 being shown fitted to thestub axles 14. The rotation of the vacuum chamber assembly 10 around theprecession axis is controlled by precession control devices such asdampers or actuators as is well known and the precession bearing stubs14 also include precession damper or actuator mounts 16. The flywheel 11is mounted on, fixed to or, as shown, integrally formed with theflywheel shaft 19, which is, in turn, located relative to the housing 13by upper spin bearing 21 and lower spin bearing 23 such that theflywheel 11 can rotate relative to the housing about the spin axis 20,driven by the spin motor 25. The upper spin bearing 21 is positionedwithin the upper spin bearing chamber 22 and similarly the lower spinbearing 23 is positioned within the lower spin bearing chamber 24.However, recirculating oil lubrication systems are not typicallypossible in gyrostabilisers in which the flywheel shaft 19 is nominallyvertical (i.e. in use oscillating up to +/−70 degrees for example eitherside of vertical) since the shaft seals between the vacuum chamber 12and the spin bearing chambers 22, 23 have unavoidable leakage due tohigh surface speed and large runout, as discussed above; hence, thetypical use of grease in such applications since it holds in place. Thepresent arrangement of an oil circuit and an air circuit is leakagetolerant, enabling oil leakage from the bearing chambers into the vacuumchamber to be purged back into the oil circuit. A radial throwing disc69 is located in an oil collection chamber 60 and fixed to the flywheelshaft 19.

FIG. 2 shows the lubrication arrangement or oil circuit 30 providinglubrication and cooling of the spin bearings which in this example arethe upper spin bearing 21, first lower spin bearing 31 and second lowerspin bearing 32. The second lower spin bearing can be a bearing typesuited to large thrust loads to support the flywheel (omitted forclarity). In the Figures, common reference numerals are used for similaror equivalent features.

FIG. 2 also shows seals 33, 34 between the bearing chambers 22, 24 andthe vacuum chamber 12 to allow the bearing chambers to be at a differentpressure to the vacuum chamber and to prevent free flow of thelubrication oil into the vacuum chamber. There are two primary benefitsof the bearing chambers being at a different pressure to the vacuumchamber: firstly, pumping oil out of a vacuum chamber is notstraightforward due, for example, to cavitation; and secondly, thepressure differential between the vacuum chamber 12 and a spin bearingchamber 22 or 24 can assist with energising of the seal 33 or 34. Theseals 33, 34 are located around the flywheel shaft (the flywheel shaftomitted for clarity in FIG. 2) and can be any rotary shaft seal.

Oil is pumped from the oil reservoir 36 by a supply oil pump 37 througha filter 38 and then an oil cooler or heat exchanger 39. The oil cooler39 is shown as two heat exchanger units 40, 41 in series with coolantflow in though conduit 42 and out through conduit 44. Oil exits the heatexchanger and the flow is then split between a conduit 50 towards theupper spin bearing chamber 22 and a conduit 51 towards the lower spinbearing chamber 24. Cooling the oil before it passes through and aroundthe spin bearings helps to cool the spin bearings at the point of heatgeneration and provides cooling not possible with grease lubrication.The oil reservoir can also act as a passive cooling tank.

The conduit 50 towards the upper spin bearing chamber 22 then branchesagain into conduit 52 through restriction 53 to outlets or nozzles 54spraying jets of oil onto the upper spin bearing 21, and to conduit 55through restriction 56 to nozzles 57 spraying jets of oil onto the uppershaft seal 33. Drain lines 58, can be one or more lines connected toopposite ports perpendicular to the orientation of the precession axissuch that oil drains out of the two ports alternately as the vacuumchamber assembly precesses. In the schematic of FIG. 2, three drainlines 58 are shown, two from the regions under opposite sides of theupper spin bearing 21 and one from the seal region, all joining intodrain conduit 59 passing through the housing 13 out of the vacuumchamber 12 and down to the oil collection chamber 60.

The conduit 51 towards the lower spin bearing chamber 24 similarlybranches out again into conduit 62 through restriction 63 to outlets ornozzles 64 spraying jets of oil onto the first lower spin bearing 31,and to conduit 65 through restriction 66 to nozzles 67 spraying jets ofoil onto the second lower spin bearing 32. Although not shown in FIG. 2,jets of oil can be sprayed up onto the lower shaft seal 34. Therestrictions 53, 56, 63, 66 and/or the number of nozzles 54, 57, 64, 67can be used to balance the flow of oil pumped to the different bearingsand seals. Drain lines 68 show the drain path of oil draining out of thelower spin bearings 31, 32 into the oil collection chamber 60. A radialthrowing disc (not shown in FIG. 2. Radial throwing disc 69 is shown inFIG. 1) can optionally be used in the oil collection chamber 60 to throwany oil in the chamber radially towards the radial ports 70 to whichreturn oil conduits 71 are connected. Such a radial throwing disc ispreferably driven by, and ideally fixed to, the flywheel shaft. In eachreturn oil conduit is a filter 73, a return oil pump 75 and a non-returnvalve 77. As the oil collection chamber 60 is at a similar pressure tothe spin bearing chambers 22, 24, i.e. between atmospheric pressure andthe vacuum chamber pressure, then pumping oil out of the oil collectionchamber, then pumping oil out of the oil collection chamber can bedifficult, but the use of a radial throwing disc can help oil enter thereturn oil conduits and thus assist the operation of the return oilpumps 75. The output of the return oil conduits is connected to the oilreservoir 36 by conduit 79. The return oil pumps 75 can be electricallydriven, or if located in the oil collection chamber 60 to avoid any needfor a radial throwing disc, can alternatively be mechanically driven bythe flywheel shaft. Various types of pump can be suitable, includinggear, screw, diaphragm or piston pumps or other types of pump that canpump a mixed flow, i.e. typically an oil and air foam. The oil reservoirfunctions most importantly as an oil de-aerator, but can provide otherfunctions such as allowing contaminants to settle out and/or to providepassive cooling of the oil.

Any oil drawn past the upper or lower shaft seals 33, 34 into the vacuumchamber 12 accumulates in the bottom of the vacuum chamber and collectsin the oil scavenge cavity 80. However, pumping the oil out of thevacuum chamber oil scavenge cavity 80 can again be difficult due tocavitation. The pumping arrangement 81 uses the pressure differencesbetween the vacuum chamber 12, the oil collection chamber 60 (and spinbearing chambers) and atmosphere to pump oil from the vacuum chamber oilscavenge cavity 80 to the oil collection chamber 60. Upper valve 82which can be a switchable one-direction valve or lockout valve,selectively allows the vacuum chamber oil scavenge cavity 80 to beconnected to an intermediate tank 83. Similarly, lower valve 84selectively allows the intermediate tank to be connected to the oilcollection chamber 60 via oil return conduit 88. Conduit 89 is an airpressure conduit that is shown in the air circuit 90 in FIG. 3 and isused to change the pressure in the intermediate tank 83.

The pumping arrangement 81 of the upper valve 82, intermediate tank 83,lower valve 84 and oil return conduit 88 can be seen again in FIG. 3along with the remainder of the components which are part of the aircircuit 90. In FIG. 3, the oil conduits are shown in as thinner linescompared to the air conduits. The pressure switching valve 91 switchesthe communication of the air pressure conduit 89 between the lowpressure in the vacuum chamber 12 (via conduit 95 and port 96 in thehousing 13) and the atmospheric pressure in air conduit 92 connected toair dryer 93 (and ultimately to atmosphere at 94). Upper valve 82 can beeither normally open or preferably, as shown, normally closed and thenselectively opened to allow oil to drain from the vacuum chamber oilscavenge cavity 80 into the intermediate tank 83. Ideally a level sensoris provided in the intermediate tank to determine when the quantity ofoil in the tank needs to be reduced, at which time, with the upper valve82 closed, the pressure switching valve 91 can connect the intermediatetank to atmospheric pressure. Then either the pressure switching valve91 remains connecting the intermediate tank to atmospheric pressure andthe lower valve 84 is momentarily opened, or the pressure switchingvalve 91 is closed and the lower valve 84 momentarily opened to connectthe intermediate tank 83 with the oil collection chamber 60. In eithercase the pressure differential of the air at atmospheric pressure in theintermediate tank 83 compared to the partial vacuum in the oilcollection chamber 60 drives oil along the oil conduit 88 out of theintermediate tank and into the oil collection chamber. Once the lowervalve 84 is closed, the pressure switching valve 91 can communicate theintermediate tank with vacuum chamber again to equalise the pressuresand permit oil to once again drain from the vacuum chamber into theintermediate tank 83 when upper valve 82 is opened. As the volume of theintermediate tank is typically 4 orders of magnitude smaller than thevacuum chamber, the pumping cycle of valve operations described can becompleted several times before the vacuum pump needs to extract the airintroduced at the end of each cycle when the intermediate tank iscommunicated with the vacuum chamber via the pressure switching valve91. Vacuum pump 97 draws air out of the vacuum chamber 12 through port98 in the housing and conduit 99. The vacuum chamber is kept close to −1bar gauge (minus 1 bar gauge or 1 bar below atmospheric pressure). Forexample, the vacuum chamber may, in use, be at a pressure of less thanminus 0.2 bar gauge or 600 Torr (mmHg), but at that pressure airfriction at the periphery of the flywheel generates heat and requiresmore power to rotate the flywheel, although the heat can be transferredby convection to the housing which in turn can be cooled. However, toavoid those issues, in use, the vacuum chamber is preferably at apressure of less than −0.73 bar gauge (200 Torr), or less than −0.8 bargauge (150 Torr), or preferably less than −0.9 bar gauge (75 Torr), andmore preferably less than −0.93 barg (50 Torr).

The other portion of the air circuit controls the pressure in the oilreservoir 36 and the pressure in the upper and lower spin bearingchambers 22, 24. The oil reservoir 36 is vented from a port 110 at ornear the top of the reservoir, through reservoir pressure conduit 111via an oil trap 112 to vent relief valve 113 which is typically set atapproximately 0.2 bar. The vent relief valve vents to atmosphere eitherdirectly or back through the dryer and ensures that the pressure in theoil reservoir is a maximum of 0.2 bar gauge. The oil trap 112 isoptional but when provided can help to ensure that oil does not passthrough the vent relief valve 113. Port 114 at the bottom of the oiltrap 112 is connected to conduit 115 in which there is a pressureregulating valve 116 to regulate the pressure of the air inlet into thespin bearing chambers. When the oil trap 112 is provided, this alsopermits oil from the oil trap to be returned to one of the volumes fromwhich oil is drained and/or pumped back to tank. In this example, thepressure regulating valve 116 is connected to port 118 on the housinginto the upper spin bearing chamber 22, so if the pressure regulatingvalve is a check valve set to open at a differential pressure of 0.7 barand the pressure in the reservoir 36 (and the reservoir pressure conduit111 and oil trap 112) is 0.2 bar gauge, then the pressure in the upperspin bearing chamber 22 will be approximately −0.5 bar gauge. The upperand lower bearing chambers 22, 24 are connected via the oil collectionchamber 60 and the drain conduit. The pressure in the bearing chamberscan be between the vacuum chamber pressure and atmospheric pressure, butpreferably higher than −0.8 bar gauge to prevent unnecessarydifficulties in pumping oil back to the reservoir. Preferably, in use,the pressure in the bearing chambers 22, 24 is between −0.2 bar gaugeand −0.8 bar gauge, more preferably between −0.3 bar gauge and −0.7 bargauge and yet more preferably between −0.4 bar gauge and −0.6 bar gauge.

When the gyrostabiliser is not in use, i.e. when the flywheel is notspinning, then it is advantageous that the pressure in the spin bearingchambers 22, 24 rises closer to atmospheric pressure, generating anincrease in the pressure differential across the shaft seals 33, 34 andthus energising them more positively onto the flywheel shaft to a levelthat together with the lack of rotation, provides improved sealing tomaintain the vacuum in the vacuum chamber for extended periods ofnon-use. Bleed back conduit 120 is connected to the oil trap returnconduit 115 by bleed back check valve 121 to enable a slow bleed of airinto the bearing chambers and without the return oil pumps (75 in FIG.2) operating to keep drawing the pressure in the bearing chambers down,the pressure gradually rises. When the return oil pumps of the oilcircuit shown in FIG. 2 are operating, they are pumping a mixed flow,i.e. oil and air typically mixed together as a foam, which results inthe return oil pumps effectively pumping air out of the bearing chambers22, 24 as well as oil, but only oil is pumped back into the bearingchambers, hence the ability to regulate the pressure in the bearingchambers by a system of passive valves such as the check valves andpressure relief valves shown in the air circuit in FIG. 3.

FIG. 4 shows the coolant circuit 130 in which coolant pump 131 pumpscoolant around the circuit. A header tank or coolant reservoir 132 isprovided for expansion and maintenance. The coolant passes through seawater heat exchanger 133 which is cooled by the flow of sea water (orfresh water if operating in fresh water) in through conduit 134 and outthrough conduit 135, unless bypass valve 136 directs the coolant flowwholly or in part through the bypass conduit or passage 137. Ideally thecoolant system is regulated to a predetermined temperature, such as 40degrees, to help manage tolerances by minimising changes in bearingclearances and by maintaining a known oil viscosity for example throughminimising operating temperature changes. The bypass valve 136 can beelectronically controlled in dependence on a sensed temperature of oneor more components of the gyrostabiliser and the sea water for example,or can be a mechanical type thermal bypass valve. In either case thebalance of coolant flow through conduit or passage 138 and the sea waterheat exchanger or through the bypass conduit or passage 137 is varied asa function of temperature.

In the example in FIG. 4, the coolant flows through a jacket 139 for thespin braking resistor (not shown) and a bypass 140 around the spinbraking resistor cooling jacket 139, controlled by an orifice 141, thenthrough a cooling plate or jacket 142 for the spin motor.

The coolant can flow in series, or as shown in FIG. 4 in parallel,through a cooling jacket 143 for the upper spin bearing and a coolingjacket 144 for the lower spin bearing.

In FIG. 4 two oil coolers or heat exchangers are shown, the lubricationoil heat exchanger 39 shown also in FIG. 2, and the hydraulic oil heatexchanger 151. The lubrication oil heat exchanger 39 comprises the twoheat exchanger units 41 and 40 as shown also in FIG. 2. Coolant entersthe first heat exchanger unit 41 from conduit 42, passes along thecoolant flow path through the heat exchangers including conduit 43, andexits the other heat exchanger unit 40 into conduit 44, from where thecoolant returns to the start of the circuit. The hydraulic oil heatexchanger 151 could be part of the coolant circuit, but is preferablycooled directly by sea water as shown in FIG. 4. The hydraulic manifold152, which can be part of a precession control arrangement providingdamping or active control, passes hydraulic oil through the heatexchanger 151 through hydraulic oil inlet conduit 153 and hydraulic oiloutlet conduit 154. Sea water, in this example, also passes through theheat exchanger 151 from the conduit 135, the sea water leaving throughconduit 156.

The coolant circuit can therefore cool the outside of the spin bearingsby jackets around the bearings and cool the inside of the bearings bycooling the oil that passes through the bearings. So in addition toreducing noise through oil lubrication, heat in the bearings iscontrolled, reducing tolerance issues through limiting thermal expansionand improving life. Further improvements to noise and especially lifeare provided by through the action of the oil washing particulates andcontaminants out of the bearings, such debris then being filteredthrough filtration of the oil in the oil circuit.

The bearings can be roller bearings or hydrodynamic bearings such aswhite metal plain bearings. Plain bearings are not typically able tooperate at the high loads and rotational velocities of gyrostabiliserflywheel shafts with grease lubrication and oil lubrication has not beenpossible until the improvements detailed herein, such as using bearingchambers at a pressure between the vacuum chamber and atmosphere andusing a pumping arrangement to pump oil accumulating in the bottom ofthe vacuum chamber out of the vacuum.

Methods other than that disclosed can be used to pump oil out of thevacuum chamber, but most are much less reliable than the solenoid valveand intermediate tank arrangement proposed, since pumping oil out fromless than −0.7 barg is problematic using existing pumps.

If the return oil pump (or pumps) for the oil in the oil collectionchamber under the lower bearing chamber is located in a conduit as shownin FIG. 2, the provision of the radial throwing disc shown in FIG. 1 canbe beneficial to try to prime the pump and improve service life sincethe pump is operating with up to a −0.7 bar pressure at inlet comparedto outlet.

Other modifications and variations as would be apparent to a skilledaddressee are deemed to be within the scope of the present invention.

We claim:
 1. A gyrostabiliser including a vacuum chamber assemblycomprising: a flywheel enclosed within a vacuum chamber formed by ahousing; a flywheel shaft fixed to or integral with the flywheel andlocated relative to the housing by upper and lower spin bearings whichpermit rotation of the flywheel about the spin axis, wherein the vacuumchamber assembly further comprises: an upper spin bearing chamber and anupper shaft seal around the flywheel shaft, the upper spin bearingchamber accommodating the upper spin bearing, and being separated fromthe vacuum chamber by the upper shaft seal, allowing the upper spinbearing chamber to be maintained at a different pressure to the vacuumchamber, a lower spin bearing chamber and a lower shaft seal around theflywheel shaft, the lower spin bearing chamber accommodating the lowerspin bearing, and being separated from the vacuum chamber by the lowershaft seal, and wherein the gyrostabiliser comprises an oil circuithaving at least one outlet into the upper spin bearing chamber, at leastone drain out of the upper spin bearing chamber, at least one outletinto the lower spin bearing chamber and at least one drain out of thelower spin bearing chamber.
 2. The gyrostabiliser of claim 1, whereinthe vacuum chamber is, in use, at a pressure of less than minus 0.8 bargauge.
 3. The gyrostabiliser of claim 1, wherein the upper and lowerspin bearing chambers are, in use, at a pressure of less than minus 0.2bar gauge and more than minus 0.8 bar gauge.
 4. The gyrostabiliser ofclaim 1, wherein each of the at least one outlet comprises at least onenozzle.
 5. The gyrostabiliser of claim 1, wherein the at least oneoutlet into the upper spin bearing chamber provides at least one oil jetor spray directed onto the upper spin bearing.
 6. The gyrostabiliser ofclaim 1, wherein the at least one outlet into the upper spin bearingchamber provides an oil jet or spray directed onto the upper shaft seal.7. The gyrostabiliser of claim 1, wherein the at least one outlet intothe lower spin bearing chamber provides an oil jet or spray directedonto the lower spin bearing.
 8. The gyrostabiliser of claim 1, whereinthe lower spin bearing comprises a first lower spin bearing and a secondlower spin bearing and wherein the at least one outlet into the lowerspin bearing chamber provides an oil jet or spray directed onto thefirst lower spin bearing and an oil jet or spray directed onto thesecond lower spin bearing.
 9. The gyrostabiliser of claim 1, wherein theat least one outlet into the lower spin bearing chamber provides an oiljet or spray directed onto the lower shaft seal.
 10. The gyrostabiliserof claim 1, wherein the oil circuit comprises at least one filter. 11.The gyrostabiliser of claim 1, further comprising an oil collectionchamber, an oil reservoir, at least one return oil pump and a supply oilpump.
 12. The gyrostabiliser of claim 11, wherein the oil collectionchamber is formed at least in part by the housing.
 13. Thegyrostabiliser of claim 11, wherein the at least one drain out of theupper spin bearing chamber and the at least one drain out of the lowerspin bearing chamber are connected to the oil collection chamber. 14.The gyrostabiliser of claim 11, further comprising a radial throwingdisc located in the oil collection chamber and fixed to or driven by theflywheel shaft.
 15. The gyrostabiliser of claim 11, wherein the oilcircuit comprises: the oil reservoir; the supply pump connected betweenthe oil reservoir and the at least one outlet into each bearing chamber;a drain conduit connecting the at least one drain out of the upper spinbearing chamber to the oil collection chamber and a drain path from theat least one drain out of the lower spin bearing chamber to the oilcollection chamber; the at least one return oil pump being provided topump oil from the oil collection chamber to the oil reservoir.
 16. Thegyrostabiliser of claim 15, further comprising an oil cooler.
 17. Thegyrostabiliser of claim 11, further comprising a vacuum chamber oilscavenge cavity located in the housing towards the bottom of the vacuumchamber.
 18. The gyrostabiliser of claim 17, wherein the vacuum chamberoil scavenge cavity is connected to the oil collection chamber by apumping arrangement.
 19. The gyrostabiliser of claim 18, wherein thepumping arrangement comprises: an intermediate tank; a lower valve forselectively communicating the intermediate tank to the oil collectionchamber; an upper valve for selectively communicating the vacuum chamberoil scavenge cavity to the intermediate tank; and a pressure switchingvalve for selectively communicating the intermediate tank with thevacuum chamber or atmosphere.
 20. The gyrostabiliser of claim 11,further comprising an air circuit comprising: a vacuum pump in fluidcommunication with the vacuum chamber, and an air dryer.
 21. Thegyrostabiliser of claim 20, wherein the air circuit further comprises apressure switching valve and an intermediate tank and: a conduitconnecting the pressure switching valve to the air dryer, a conduitconnecting the pressure switching valve to the intermediate tank, and aconduit connecting the pressure switching valve to the vacuum chamber.22. The gyrostabiliser of claim 20, wherein the air circuit furthercomprises a vent relief valve connected by a reservoir pressure conduitto a port at or toward a top of the oil reservoir.
 23. Thegyrostabiliser of claim 22, wherein the air circuit further comprises apressure regulating valve connected between the reservoir pressureconduit and a port on the housing.
 24. The gyrostabiliser of claim 23,wherein the air circuit further comprises an oil trap in the reservoirpressure conduit between the vent relief valve and the oil reservoir,the pressure regulating valve being connected to the reservoir pressureconduit by a port toward a base of the oil trap.
 25. The gyrostabiliserof claim 22, wherein the air circuit further comprises a bleed backcheck valve between the reservoir pressure conduit and the air dryer.26. The gyrostabiliser of claim 1, further comprising a coolant circuitcomprising: a coolant pump; a coolant reservoir; at least one oil heatexchanger; and a water heat exchanger.
 27. The gyrostabiliser of claim26, wherein the coolant circuit further comprises a cooling jacket forthe upper spin bearing and a cooling jacket for the lower spin bearing.28. The gyrostabiliser of claim 26, wherein the coolant circuit furthercomprises a cooling plate or jacket for one or more of a spin motor, aspin motor drive, a precession motor and a precession motor drive. 29.The gyrostabiliser of claim 26, wherein the coolant circuit furthercomprises a cooling jacket for the spin braking resistor.
 30. Thegyrostabiliser of claim 26, wherein the cooling circuit furthercomprises a bypass conduit or passage in parallel with a coolant flowpath through the water heat exchanger and a bypass valve for controllingthe balance of coolant flow through the bypass conduit or passage andthrough the coolant flow path through the water heat exchanger.
 31. Thegyrostabiliser of claim 26, wherein the at least one oil heat exchangercomprises a lubrication oil heat exchanger having an oil inlet and anoil outlet forming part of the oil circuit.
 32. The gyrostabiliser ofclaim 26, wherein the at least one oil heat exchanger comprises ahydraulic oil heat exchanger having a hydraulic oil inlet and ahydraulic oil outlet forming part of a hydraulic circuit comprising ahydraulic manifold.
 33. A lubrication arrangement for a vacuum chamberassembly for a gyrostabiliser, the vacuum chamber assembly comprising: aflywheel enclosed within a vacuum chamber formed by a housing; aflywheel shaft fixed to or integral with the flywheel and locatedrelative to the housing by upper and lower spin bearings which permitrotation of the flywheel about the spin axis, an upper spin bearingchamber and an upper shaft seal around the flywheel shaft, the upperspin bearing chamber accommodating the upper spin bearing and beingseparated from the vacuum chamber by the upper shaft seal, allowing theupper spin bearing chamber to be maintained at a different pressure tothe vacuum chamber, a lower spin bearing chamber and a lower shaft sealaround the flywheel shaft, the lower spin bearing chamber accommodatingthe lower spin bearing, and being separated from the vacuum chamber bythe lower shaft seal, wherein the lubrication arrangement provides atleast one oil jet or spray into the upper spin bearing chamber and atleast one oil jet or spray into the lower spin bearing chamber.
 34. Asystem for lubricating a spin bearing of a gyrostabiliser, the systemcomprising a lubrication circuit, a coolant circuit and an air circuit.35. The system of claim 34, wherein the lubrication circuit comprises atleast one outlet for releasing lubricating oil into a bearing chamberhousing the spin bearing.
 36. The system of claim 35, wherein thecoolant circuit comprises at least one lubricating oil heat exchangerfor drawing heat out of the lubricating oil of the lubricating circuit.37. The system of claim 35, wherein the coolant circuit comprises a pumpand a water heat exchanger for drawing heat out of coolant in thecoolant circuit.
 38. The system of claim 35, wherein the air circuitcomprises: a vacuum pump for drawing air out of the vacuum chamber; andvalves to control a pressure in the bearing chamber to be between apressure in a vacuum chamber of the gyrostabiliser and an atmosphericpressure.
 39. The system of claim 35, further comprising an intermediatetank having an upper oil port, an upper air port, a lower oil port and alevel sensor, wherein the lubrication circuit further comprises a firstlockout valve between the upper oil port of the intermediate tank and aport towards a bottom of a vacuum chamber of the gyrostabiliser and asecond lockout valve between the lower oil port of the intermediate tankand an oil collection chamber of the gyrostabiliser, the air circuitcomprising a pressure switching valve to selectively communicate aconduit connected to the upper air port of the intermediate tank toeither the vacuum chamber of the gyrostabiliser or to atmosphere.